The present invention relates to a device and to a machine intended especially for the preparation of drinks based on milk, such as, for example, cappuccino, hot milk, chocolate and the like.
To be more precise, the present invention relates to a device and to a machine which are intended both for use in the catering industry, such as, for example, in bars or restaurants, and for domestic use.
As is known, both machines intended for public use and machines intended for domestic use comprise a water-heater for the production of steam which is directed to an emitting member or nozzle. The steam is sent from the latter through the liquid to be heated.
The most characteristic and valued aspect of milk-based drinks, in particular cappuccino, is the presence of foam, which is obtained by emulsifying milk and air. In particular, the more dense and compact the foam is, that is to say, the more numerous, small and intimately dispersed in the milk the air bubbles are, the more the drink is appreciated.
The emulsification stage for obtaining the foam normally takes place during the stage of heating the milk, that is to say, as the steam is being sent through the milk to be heated and emulsified.
It is now common practice to utilise the suction effect produced by the steam leaving the nozzle in order to draw air into the liquid phase of the milk, while the steam heats the milk and is condensed therein or dispersed.
That sequence of stages can be entrusted, for example, to the dexterity of the operator, with the consequence that the density and compactness of the foam depend largely on his or her skill.
It has been found that the final result depends both on the position of the nozzle and on the level of the liquid phase in the milk. It has also been found that the cyclic movement of lifting and lowering the container of milk relative to the steam nozzle promotes the fractionation of the air and its intimate dispersion in the liquid phase, but increases the risk of milk being splashed and spilt.
The disadvantages mentioned above are even more evident in the case of machines for domestic use owing both to the lack of experience on the part of the operator and to the use of limited amounts of milk, and to the small dimensions of the machine and therefore the small amount of steam which can be supplied.
Therefore, a great need is felt in this field to avoid the disadvantages of the manual procedure and in particular to simplify the operations involved. Consequently, devices have been provided for heating and emulsifying liquids, in particular milk, that do not require the presence of an operator with special experience.
For example, a first type of device for heating and emulsifying is known which is constituted by a chamber arranged around the steam nozzle and provided with an opening for the entry of air, an opening for the entry of milk and an opening for the discharge of emulsion.
The functioning known hitherto of those devices provides that the emission of steam produces a partial vacuum inside the chamber which causes the milk and air to be drawn into it. An emulsion of milk, air and steam which leaves via the discharge opening is thus formed in the chamber. Although the three openings corresponding to the entry of milk, the entry of air and the discharge of emulsion are separate, the chamber is constituted by a single space through which milk, air and emulsion pass in a substantially random and turbulent manner.
Another type of device for heating and emulsifying is known and is constituted by a turbulence tube fitted to the end of the steam nozzle and having an opening for the entry of air. The end of the turbulence tube remote from the nozzle is open and is immersed in the liquid to be emulsified. The jet of steam, by pushing the liquid downwards, generates a partial vacuum inside the tube which, on the one hand, draws air through the above-mentioned inlet and, on the other hand, draws liquid through the open end. A turbulent movement of liquid, air, steam and emulsion is therefore created inside the tube. The emulsion is forced by the jet of steam through the open end of the turbulence tube, generating, through that opening, an incoming flow of liquid and an outgoing flow of emulsion.
As is known, although the types of device indicated above simplify the operations of heating and emulsifying a liquid, they are not free from disadvantages.
In the first place, the dimensions of the air particles inside the liquid phase are rather large, with the result that the density, the compactness and the stability of the emulsion over time are not optimum. That disadvantage could be attributable to the establishment of movement or turbulent circulation inside the chamber or turbulence tube which, while agitating the liquid, does not succeed in adequately fragmenting and intimately dispersing the air inside it.
In the second place, the known devices have the disadvantage of being difficult to clean and therefore of being rather unhygienic, areas and recesses being present in which the liquid to be emulsified can settle and coagulate.
In addition, although the opening for the entry of air is generally positioned at some distance from the inlet for liquid, the liquid may rise as far as the air inlet opening and partially block it, thus changing the proportions of air and liquid to be emulsified. In addition, small modifications in the air flow rate have a detrimental effect on the quality of the emulsion obtained, since this quality depends on a precise proportional ratio worked out between the amount of air sucked in and the amount of liquid processed by the device.
In addition to the above, the known devices provide that the steam nozzle, and in particular the steam outlet orifice, be arranged near the inlet for the liquid. That structure has the further disadvantage of the formation of scale along the steam duct. This is caused by the fact that the liquid can rise along the steam nozzle as far as the tap which cuts it off, as a result of the effect of the almost instantaneous partial vacuum generated by the cooling by immersion in cold milk of the duct carrying steam that is saturated or almost at atmospheric pressure. The immediate suction generates a spurt of cold milk which rises through the nozzle and along the steam duct and which causes the almost instantaneous condensation of the entire volume of saturated or slightly unsaturated steam which was occupying the cavities leading from the nozzle as far as the barrier represented by a tap which normally cuts off the pressure and brings about the supply of steam.
Finally, the known devices have a structure which is rather complicated to produce, above all in the case of the first type of device discussed above. In that structure, the openings for the entry of milk and the discharge of emulsion are rather small in an attempt to keep them as separate as possible, thus preventing the processing of large amounts of liquid and therefore increasing the emulsification times.
The problem on which the present invention is based is to propose a device for heating and emulsifying liquids, in particular drinks, and a machine for the preparation of hot drinks, which device and machine have structural and functional characteristics such as to satisfy the above-mentioned requirements and, at the same time, to overcome the above-mentioned disadvantages discussed with reference to the prior art.